[BUG]

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: Invalid signature in thinking block"},"request_id":"req_011CcQ4mtahApfU9cBhqc8Zi"}

What Should Happen?

⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: Invalid signature in thinking block"},"request_id":"req_011CcQ4mtahApfU9cBhqc8Zi"}

Error Messages/Logs

⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: Invalid `signature` in `thinking` block"},"request_id":"req_011CcQ4mtahApfU9cBhqc8Zi"}

Steps to Reproduce

⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: Invalid signature in thinking block"},"request_id":"req_011CcQ4mtahApfU9cBhqc8Zi"}

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

⎿  API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.1.content.0: Invalid signature in thinking block"},"request_id":"req_011CcQ4mtahApfU9cBhqc8Zi"}

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_